The present invention relates to a one-trip squeeze pack system used in gravel pack, frac pack, and similar applications in oil field wells. Specifically, the present invention allows for gravel pack, frac pack, or similar assemblies to be run on the production string, thus eliminating the need for a separate trip down the well with a work string.
Gravel pack assemblies and frac pack assemblies are commonly used in oil field well completions. A frac pack assembly is used to stimulate well production by using liquid under high pressure pumped down a well to fracture the reservoir rock adjacent to the wellbore. Propping agents suspended in the high-pressure liquid (in hydraulic fracturing) are used to keep the fractures open, thus facilitating increased flow rates into the wellbore. Gravel pack completions are commonly used for unconsolidated reservoirs and for sand control. Gravel packs can be used in open-hole completions or inside-casing applications. An example of a typical gravel pack application involves reaming out a cavity in the reservoir and then filling the well with sorted, loose sand (referred to in the industry as gravel). This gravel pack provides a consolidated sand layer in the wellbore and next to the surrounding reservoir producing formation, thus restricting formation sand migration. A slotted or screen liner is run in the gravel pack which allows the production fluids to enter the production tubing while filtering out the surrounding gravel.
A typical gravel pack completion is illustrated in FIG. 1. FIG. 1 is a schematic representation showing a perforated wellbore annulus 2, with perforation shown extending into the zone of interest 5. Within the wellbore annulus 2 a tube 4 has been placed on which is attached a screen 6. The gravel 3 is shown packed into the perforations in the zone of interest 5 and surrounding the screen 6. The gravel 3 is an effective filter of formation fluids, because the formation sand which flows with the production fluid is largely trapped in the interstices of the gravel.
One specific type of gravel pack procedure is called a squeeze gravel pack. The squeeze gravel pack method uses high pressure to xe2x80x9csqueezexe2x80x9d the carrier fluid into the formation, thereby placing gravel in the perforation tunnels of a completed well and the screen/casing annulus. The frac pack method is very similar, except the xe2x80x9csqueezexe2x80x9d is carried out at even higher pressures with more viscous/heavier fluid in order to fracture the reservoir rock. Consequently, the down-hole assembly used for these two procedures is frequently the same.
Typical gravel pack or frac pack assembly is presently run into the well on a work string. The work string is a length of drill pipe normally removed from the well once the packing job is complete. The work string assembly also contains a setting tool for the packer and a crossover tool to redirect the treatment from within the work string into the formation. This assembly usually requires a setting ball to be dropped from the surface which must fall to a seat on the assembly. The setting ball actuates the setting tool and xe2x80x9csetsxe2x80x9d the packer, thus isolating the assembly from the upper wellbore. In some applications it establishes the crossover in the crossover tool as well. It sometimes occurs in these prior art applications that the ball is lost or damaged. Seat damage and/or debris may also cause seating problems. Further, it takes time for the ball to fall. Most importantly, the setting and crossover tools must be pulled from the well before the seal assembly and tubing may be run. This means the entire work string is removed from the well and a separate production string, through which the production fluids or gases will flow, is then landed back in the well. All this takes considerable rig time and adds to the expense of the completion. This additional time may also expose the well to fluid losses and result in formation damage. Rental and redress fees are usually charged for the use of these tools which adds to the expense of the job.
A need exists, therefore, for a gravel pack, frac pack and like assembly systems that can be run into the well on a work string that will also act as the production string (a xe2x80x9cone-tripxe2x80x9d assembly). This would eliminate the need for a separate work string to be run in and out of the well and save considerable rig time while greatly reducing sealing problems encountered under the present art.
The present invention relates to an improved gravel pack, frac pack, and like assemblies that can be run into the well on production tubing, thus saving one trip with a work string and avoiding seating problems inherent with prior art methods and assemblies. Because of the invention design, there is no setting tool required. The setting mechanism is within the invention""s packer. There is no cross-over tool required either. The gravel pack cross-over is an integral part of the service seal unit which is run in with the assembly and remains in the well. The design of the system combined with the fact that the system is run on production tubing makes the chance of sealing problems or disrupting the setting of the packer negligible.
Unlike the prior art, the packing components of the instant invention remain in the well after the packing procedure is complete. The same components are then used for the production phase. Therefore, the present invention eliminates the need for a separate run with a work string and the retrieval of special tools after packing.
The present invention uses a unique service seal unit design using concentric tubing, with the inner tubing an extension of the traditional wash pipe and later acts as the production tubing. The inner tubing contains a ported sub which can be isolated at various positions within the outer tubing by way of seals located above and below the ported sub. The service seal unit can be raised and lowered on the work/production string and isolated at various positions in order to accomplish setting the packer, running a packing job, reversing out packing fluids, and receiving production fluids. No rotation is required to shift from one position to the next. The positions are located by simply raising or lowering the production string.
The invention is versatile and can be tailored to meet the requirements of each specific well completion. If some components are not desired, the system can be modified to include only those that fit a particular application. The invention provides a means for carrying screens into the well which makes it applicable to unconsolidated formations. It provides a reverse/spot position that minimizes fluid injection into the formation and allows excess slurry to be removed from the wellbore by reverse circulation. This spot/reverse position can be positively located by use of an optional indicator collet. The packer may be either permanent or retrievable and can be set without tubing manipulation or the potential that it will release during the pumping procedure.
The present invention is a great improvement over prior art methods and assemblies by eliminating the well completion step of running a packing job on a separate work string which must be run down the well and then run back up, thus exposing the well to seal problems, potential fluid loss, and using expensive rig time. Using a functionally simple design, the present invention saves rig time, eliminates sealing and fluid loss problems, and provides an economical alternative to prior art frac pack, gravel pack, and similar well completion assemblies.